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GCC vs. LLVM-GCC Benchmarks

09-04-2009, 08:40 AM

Phoronix: GCC vs. LLVM-GCC Benchmarks

Last Friday we published Mac OS X 10.6 benchmarks and then on Monday they were joined by Ubuntu 9.10 vs. Mac OS X 10.6 benchmarks. One of the requests that has come up since publishing those articles are to carry out a set of tests comparing the performance of LLVM and LLVM-GCC. With Apple's Snow Leopard release, some parts of the operating system were built using LLVM-GCC for optimized performance, although this compiler is not yet matured. In this article we have a set of 12 benchmarks comparing GCC to LLVM-GCC.

Last Friday we published Mac OS X 10.6 benchmarks and then on Monday they were joined by Ubuntu 9.10 vs. Mac OS X 10.6 benchmarks. One of the requests that has come up since publishing those articles are to carry out a set of tests comparing the performance of LLVM and LLVM-GCC. With Apple's Snow Leopard release, some parts of the operating system were built using LLVM-GCC for optimized performance, although this compiler is not yet matured. In this article we have a set of 12 benchmarks comparing GCC to LLVM-GCC.

This is one, I think, important note from the release notes (for LLVM 2.5 and the appropriate LLVM-GCC):

* In this release, the GCC inliner is completely disabled. Previously the GCC inliner was used to handle always-inline functions and other cases. This caused problems with code size growth, and it is completely disabled in this release.

Comment

Ouch, LLVM-GCC was beaten solidly here. Any guesses as to why? Wasn't LLVM supposed to be much faster?

Couple of factors I would guess comes into play. LLVM is fairly young in development and the biggest improvements so far as performance concerning LLVM is the time to compile. Unfortunately we haven't seen any of those compile times in the tests.

Comment

Couple of factors I would guess comes into play. LLVM is fairly young in development and the biggest improvements so far as performance concerning LLVM is the time to compile. Unfortunately we haven't seen any of those compile times in the tests.

Plus you won't see any speed advantage because phoronix is using the gcc frontend.

Comment

Couple of factors I would guess comes into play. LLVM is fairly young in development and the biggest improvements so far as performance concerning LLVM is the time to compile. Unfortunately we haven't seen any of those compile times in the tests.

Someone mentioned there could be only one core used when comes to GCC and Ubuntu vs OS X benchmarks. Btw. I heard GCC is optimized to be good at some benchmarks, but I wonder if its better results have reflection in reality.